The disclosure of Japanese Patent Application No. 2002-13273 filed on Jan. 22, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
This invention relates to an evaporated fuel processing unit in an internal combustion engine. More particularly, this invention relates to an evaporative fuel processing unit capable of trapping evaporative fuel before it is discharged into the atmosphere from an intake passage of the internal combustion engine.
2. Description of Related Art
An evaporative fuel processing unit has been put into practical use that suppresses evaporative fuel from being discharged outside by leading hydrocarbon evaporating from a fuel tank, i.e., evaporative fuel, while a vehicle is running or stopped to a charcoal canister (hereinafter simply referred to as xe2x80x9ccanisterxe2x80x9d), and then adsorbing the evaporative fuel with an adsorbent in the canister.
While the vehicle and the internal combustion engine are stopped, some fuel may leak into the intake port from the nozzle hole of an injector (i.e., fuel injection valve) provided in an intake port and a cylinder, and some fuel may adhere onto the wall of the intake port, creating a so-called fuel wet. The fuel may then evaporate and flow to the outside through an outside air opening in the air cleaner. As the regulations concerning evaporative fuel have recently become more stringent, these fuels are starting to be seen as a problem.
Further, Japanese Patent Application Laid-Open Publication No. 55-84846 discloses a system in which, in order to trap fuel that evaporates from not only a fuel tank but also a carburetor with a canister when the internal combustion engine is stopped, an intake passage on the upstream or downstream side of the throttle valve is connected to a canister provided to trap fuel that evaporates from the fuel tank. Further, this system processes the fuel by desorbing the fuel trapped in the canister while the internal combustion engine is operating and drawing the desorbed fuel into the intake passage. Because the throttle valve does not completely close off the intake passage even when the internal combustion engine is operating, however, there is a possibility that the evaporative fuel that leaks upstream from the throttle valve while the engine is stopping may be discharged into the atmosphere through the air cleaner in the case where the intake passage is connected to the canister on the downstream side of the throttle valve.
Needless to say, when the intake passage is connected to the canister on the upstream side of the throttle valve, the air cleaner provides constant communication between the intake passage from the throttle valve to the air cleaner and the atmosphere. Therefore, a large portion of the evaporative fuel accumulated in the intake passage from the throttle valve to the air cleaner is not introduced to the canister. As a result, a similar problem exists due to that portion of the evaporative fuel flowing out into the atmosphere from the outside air opening of the air cleaner.
Moreover, Japanese Patent Application Laid-Open Publication No. 54-65213 discloses a system in which a check valve is provided in the outside air opening of the air cleaner to close off the inlet to the intake passage when the internal combustion engine is stopped so as to trap evaporative fuel accumulated in the intake passage with a canister. However, a blow-by line from the crankcase of the internal combustion engine is connected to the intake passage that is closed off in this case, so unburned fuel which does not evaporate easily and which contains blow-by gas, as well as minute particles of engine oil and the like are introduced into the canister. These components adhere to the adsorbent inside the canister and lower the adsorption capability, so it is possible that the original function of the canister may be lost.
A first aspect of the invention relates to an evaporative fuel processing unit. This processing unit is provided with a passage that provides communication between an intake passage of the internal combustion engine and a canister, a passage that provides communication between a crankcase of the internal combustion engine and the intake passage, and a valve that is provided farther upstream in the intake passage than the location where those passages are connected together. This valve is able to make the downstream of the valve a substantially closed space by closing off the intake passage. Accordingly, evaporative fuel that accumulates in this intake passage will not leak out upstream of the valve and be discharged into the atmosphere. The trapped evaporative fuel passes through the passage that provides communication between the intake passage of the internal combustion engine and the canister and is adsorbed by the adsorbent in the canister.
The evaporative fuel adsorbed by the adsorbent in the canister is then desorbed by a flow of air that passes through the canister when the internal combustion engine is operating, and is introduced into the intake passage, just as it is ordinarily. After being introduced into the intake passage, that fuel is then burned in the cylinders together with fuel injected by an injector (i.e., fuel injection valve) and processed.
Moreover, because the foregoing processing unit has a valve that closes off the canister from the crankcase by closing when the engine is stopped, it is possible to minimize unburned fuel that does not evaporate easily and which contains blow-by gas from being adsorbed by the adsorbent in the canister.
xe2x80x9cMake the downstream side of the intake passage a substantially closed spacexe2x80x9d means that an exhaust pipe side may be open downstream of the valve by an exhaust valve and an intake valve of the internal combustion engine.